The PLC supports the NTP and the SNTP protocol ((Simple) Network Time Protocol). Compared to SNTP, the NTP protocol achieves higher accuracy in time synchronization, meeting advanced requirements for accuracy and reliability of a PLC solution.
In case a configured NTP protocol cannot be used, SNTP protocol is used as a fallback solution.
The S500 I/O modules do not support the functionality to create and transfer a timestamp with an event directly at the I/O channel. A workaround is using SoE logging (Sequence of Event) for a root-cause analysis. An ⮫ application example explains how events are processed.
The protocols NTP and SNTP provide the functionality to synchronize the clock of a PLC to an external time source. An ⮫ application example demonstrates how to synchronize the PLC time with a time server.
A specification of the (S)NTP protocol itself can be found in the document RFC4330.
The following modes are supported by the implementation of the PLC:
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(S)NTP client
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(S)NTP server
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(S)NTP client and server
The function block PmSntpInfo can be used to read diagnosis information of the protocol.
Refer to the documentation of the library ABB_Pm_AC500.lib for further information.
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If a high precision of system time is wanted, use a fully functional NTP server or at least an SNTP server with a high-precision time-source (e.g. DCF-77 receiver). Avoid cascading several levels of (S)NTP server / (S)NTP clients.
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Client requests are normally sent at intervals depending on the frequency tolerance of the client clock and the required accuracy. However, under no conditions requests should be sent at less than one minute intervals (see RFC 4330). Keep that in mind when setting polling-interval of the (S)NTP client, especially if a huge amount of clients use one single server.
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Be sure not to use broadcast or multicast addresses as server or backup-server since current (S)NTP implementation does not support manycast mode.